This one was actually pretty darn clever - nobody's abused it, but
I was reading a blog post where someone described this type of
issue, I realized it was a brilliant attack, and then realized
DTI was vulnerable. Oops. Thanks for the solution, Jamie!
http://jamie-wong.com/2012/08/22/what-i-did-at-khan-academy/#XSS+Fix
Many forms on the site contain a hidden authenticity_token field,
unique to each visitory. If a user submits a request with an
invalid authenticity_token, Rails assumes that it's a CSRF attempt
and logs out the user. So, if we happen to cache those forms with
authenticity_token fields, all users who use that form will have
the same authenticity_token (valid for only the first user who
saw the form, invalid for everyone else), and all requests made
through that form will log out the user. Bad news.
So, we stopped caching those forms. Yay!
I think I got the 0-width bug where the outfit never expands beyond
0px width, and there were also some issues with the fact that
image subscriptions pointed to the current outfit object, even
after that object had changed identity, so now we re-fetch from
the cache by ID.
Use the ImageMagick flatten command to generate the output all at
once instead of compositing each layer individually, and download
the layers in parallel. On my box, saving roopal27 five times took
a total of 30 seconds before, whereas now it takes 7 seconds. I
expect it to be even better on the production box, where latency
is even lower.
